The present invention is directed generally to load weigh valves for railway cars, and more particularly, to load weigh valves that are mounted to the railway truck frame.
The load weigh valve assembly is the component of the railway car that senses the load placed on the railcar body and communicates with the brake cylinders to adjust the wheel brake pressure accordingly. That is, as the car body is loaded and the springs of the suspension deflect, the load weigh valve senses this spring deflection and communicates with the brake cylinders to increase the brake pressure applied to the wheels. Likewise, as the load placed on the car body decreases, the load weigh valve communicates with the brake cylinders to decrease the amount of brake pressure applied to the wheels.
A load weigh valve is commonly used with certain types of cars, such as coal cars, boxcars, gondolas and high-speed express boxcars. It is used on these types of cars because the weight of these cars varies considerably from a lightweight, unloaded car to a much heavier loaded car and the required amount of brake pressure to be applied will vary depending on the loaded state of the car. Most load weigh valves have several pressure positions. For example, it is common for load weigh valves to have a no pressure position, a low pressure range, a changeover position and a high pressure range. The load weigh valve is in the no pressure position when the brakes are released. When the brakes are applied and the car weight is between the empty and 40% loaded condition, the valve is in the low pressure position. When the brakes are applied and the car weight is above the 40% loaded condition, the valve changes to the high pressure position. It should be apparent that the changeover position for the load weigh valve is approximately a 40% loaded condition. The low pressure position of the load weigh valve allows the brake system to apply less air pressure, and hence less brake shoe force to the wheels. Otherwise, in the light car condition (that is, less than a 40% loaded condition), without the use of a load weigh valve in a low pressure position, the full brake force would be applied to the wheels causing the wheels of the car to slide thereby creating flat spots on the tread of the wheels, a result that is undesirable.
Conventionally, the prior art load weigh valve was mounted to the railcar body and included a load weigh valve pivot arm that interfaced with the truck frame. A drawback with the conventional load weigh valve, and specifically the mounting of the load weigh valve to the car body, is that the car body is sprung relative to the truck frame. As a result, the load weigh valve, and in particular, the pivot arm of the load weigh valve, not only must sense the load placed on the railcar body, but also must compensate for spring deflection, truck swivel and car body roll. Also, the conventional mounting arrangement locates the load weigh valve on the underside of the car body floor, above the truck frame. This arrangement is difficult to inspect because the car body side sill obstructs most views of the valve. To view the valve, an inspector must position his head between the truck frame and the car body sill. Likewise, in the conventional arrangement, valve replacement or maintenance is very cumbersome and easy to overlook. Another drawback with the railcar body mounted load weigh valve is the device will not work with a primary sprung truck, such as a freight truck. On a primary sprung truck arrangement, the spring deflection occurs between the axles and the truck frame.
The present invention overcomes the aforementioned problems known in the art by providing a load weigh valve arrangement that is mounted to the truck frame and not the railcar body. In an exemplary embodiment, the present invention includes a load weigh valve assembly mounted to the truck frame, the load weigh valve assembly including a load weigh valve connected to the truck frame, a weigh valve pivot arm operatively connected to the load weigh valve, and a load sensor arm interface bracket.
With the load weigh valve assembly mounted to the truck frame, the valve senses spring deflection between the sprung and unsprung elements of a primary sprung truck arrangement. Also, the oscillating and sliding motion at the load weigh valve pivot arm, which occurs with the standard freight truck during swivel, is eliminated. In an exemplary embodiment, with the load weigh valve mounted at or near the truck frame centerline, the undesirable valve actuation that occurs due to car body roll is eliminated. In addition, the location of the load weigh valve at or near the truck centerline minimizes the exposure of the load weigh valve to foreign matter and flying debris thrown up by the wheels during operation. Finally, the assembly of the present invention is a more rugged and reliable construction of the conventional load weigh valve assembly.